LHCb results in proton-nucleus collisions at the LHC

The forward acceptance of the LHCb detector allows it to probe proton-ion collision in a unique kinematic range, complementary to the other LHC experiments. The production of $J/\Psi$ and $\Upsilon$-mesons decaying into two muons is studied at the LHCb experiment in proton-lead collisions at a proton-nucleon centre-of-mass energy $\sqrt {s_{NN}} = 5$ TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 1.6 nb$^{-1}$. The nuclear modification factor and the forward-backward production ratio are determined for $J/\Psi$ and $\Upsilon(1S)$ mesons. Clear suppression of prompt $J/\Psi$ production is observed with respect to the production in $pp$ collisions at large rapidity, while the suppression of $J/\Psi$ from $b$-hadron decays is less pronounced. The nuclear modification factor for $\Upsilon(1S)$ mesons in the forward region is found to be similar to those for $J/\Psi$ from $b$-hadron decays. Furthermore, a first observation of $Z$ bosons in proton-lead collisions is reported.